US2455838A - Air frame structure - Google Patents

Description

Dec. 7 1948. B. N. WALL'IS AIRFRAME STRUCTURE 4 Sheets-Sheet 1 Filed June 15, 1945 I jzvyeni'or 6. n waze g,

I n-4a Dec. 7,1948. B N. WALLIS AIRFRAME STRUCTURE 4 Sheets-Sheet 2 Filed June 15, 1945 flfl W H 0 0 0 Dec. 7, 1948. ALLIS 2,455,838

AIRFRAME STRUCTURE FiledJune 15, 1945 4 sheets-sheet 5 .11. Loam B1 CUM B. N. WALLIS AIRFRAME STRUCTURE Dec. 7, 1948- 4 Sheets-Sheet 4 Filed June 15, 1945 fivenzor 6. \N UJQMQ COM M, M

Patented Dec. 7, 1948 UNITED srArss PATENT OFFICE fBarnesNevilleWallis, Weybridge, England, as- Signr to ;-Vickers-Armstrongs Limited, Westminster.London England,

AppIicationJuneIS, 1945, Serial No. 599,668

In Great Britain June 19, 1944 It is well-known that in the construction of a space-containing frame having an. outer clothing or skin the most favourable position in which to put the material composing the structure is at the surfacethereof, where it will not only give the greatest strength and stiffness for its weight but also provide the necessary covering. Where, however, as in aeronautical engineering, the strength/weight ratio of a structureis of primary importance, the skin type of construction is inherently inefficient due to the incapability of thin sheet metal to resist loads in compression and shear (including torsion) without break-down of the compressive stability of the material, and consequent surface wrinkling. Inaircraft intended to fly at high speeds the preservationof laminar air flow over the body and wings is so important that even very minute wrinkles of-the surface cannot be tolerated, and although slightly curved plating can be stabilised sufliciently to prevent Wrinkle-formation by rigidly attaching the plating to a closely pitched network of stiffening members on its inner surface, or by increasing the thickness of the plating, either expedient results in a relatively poor strength/weightratio.ofpthe structure. I

Another problem arises in connection withgthe external clothing of geodetic or articulated aircraft structures. The textile fabric which has hitherto been used for this purpose, upon which the sustentation of the aircraft depends during flight, is disadvantageous inasmuch as the material is fragile and liable to accidental damage and contributes nothing to the strength or stiffness of the main structure, whilst certain difficulties are experienced in maintaining ithe required outward form of the structure unaeriaterai atmospheric pressures taken in conjunction with the variable deflection of the skeletal structure due to changes in operat onal loading. attempt to obviate thisdisadv t geodetic structure by the use of a more rigidformof m;

ering material (e. g. a thin skin of metal plating, plastic material or plywood) results in. the for'- mation of unstable wrinkles which are even more pronounced than those experienced in stressed skin construction, owing to the greater flexural movement which necessarily accompanies the higher working stresses attained in the individual frame members; the expedient of increasing.

the thickness of the plating, to .a degree such that it becomes the dominant factor-in'the stiffness and strength of the structure asa whole, would obviously stultify the use of the articulatedskeleton supporting it. No practicable method. has

8 elicits. (01. 2449117) been devised for stretching a continuous skin of rigid material to a sufliciently high tension relative to the stresses which may be induced by external loading of the skeletal structure; to do this the thickness of the plate or sheet would have to base small as to render it too susceptible to deflection under loads acting normal to the surface The present invention is directed to the provision of a novel form of material which, while avoiding the great weight of the known stressedskin construction, will serve as a covering for a geodetic or other type of articulated structure and will be capable of assuming within negligible limits of error any desired formation in spherical curvature and also of being stressed in such manner that a high degree of torsional rigidity can be exacted from the skin itself, thus enabling the skin to contribute substantially to the strength and rigidity of the internal skeleton. A secondary object'of the invention is the provision of an improved method of fabricating the skin of an airframe structure in situ.

' According to the invention a skin-like covering material for the said purpose is composed of thin metal ribbons or strips interlaced or interwoven to form a flexible fabric which may be stretched over and attached to the airframe structure. The fabric skin is preferably capable of being stressed bytauten'ing the constituent ribbons. The metal ribbons are divided into two or more systems, each having its components closely arranged in parallel, the systems being interlaced after the fashion of the warp and weft of a woven fabric, so that the surface of the interlaced material is substantially continuous and capable of having a smooth-aerodynamic finish imparted to it by successive ap-plications of a suitable paint or like sealing medium by coating or spraying, each application being rubbed down with a fine abrasive until the desired degree of. smoothness is attained.

The application of the invention to airframes of the geodetic type is hereinafter described by wayof example with reference to the accompanying drawings. In said drawings Fig. 1 is a fragmentary elevation ofv a part of an aeroplane fuselage and Fig. 2 is a plan of an aeroplane wing; in both cases the outer skin is fashioned in accordance with the method characterising the present invention. Fig. 3 is a plan of a-portion of the v.interlaced metal ribbon skin shown sep a rately. Figs. 4- and 5 are fragmentary plan views showing one method of attachment of the skinforming ribbons respectively to the terminal and intermediate-members of the supporting structure.

ner in which the skin covering provided in ac cordance with the invention is supported'a-round the leading edge of a wing.

The metal skin provided by-"the inven-tionisfl conveniently fabricated on the" structure, each ribbon being laid in place and attached in its position in turn. pre-tensioned to a high degree, by theimethods channel-section, and the web Cl is pierced by two rows of inclined slots C2, arranged in staggered pairs, so that each ribbon, as it crosses a stringer, may be secured in position thereon by being looped under the portion C3 which lies between a pair of .said slots C2.

An alternatiireimethodioffattaching the skin to the-stringers C is s-howndn Figs. 9 and 10. In this case the stringers are formed with a longitudinal recess C4 in the upper surface, and battens C5 are used to press the ribbons, Where they cross I the stringer, into the depths of said recess, the

battens ci being: finally held in place by screws and nuts C6 as shown.

In order that the ribbonszn'raist be In-Figs; 4, 6* and 7 the reference letter E indicates acterminalstringer. The ribbons A, A etc.

areattached at their ends to said member E by hereinafter described, they should be made of a high tensile steel. Corrosion can be avoided by' using ribbons of stainless steel, which material has the additional advantage of being-non mag'e ne 1c. In the embodiments illustrated in the draw ings, the skin is composed of two systems' of"-rib bons, indicatedrespe'ctively by'the' reference letters A, A etc. and B, B etc; The ribbons" of"the two systems areinterlaced' so as to -lieirrcl'ose parallel arrangement, the whole constituting an interlaced or woven fabric having a substantially continuous surface; 'A fragment" of-such= fabricated skin is shown separately inFlgfS.

Where, as in theexamples illustrated m- Figs. 1 and 2, the skin is appliedtoan airframeofthe' geodetic type, the ribbons'A, B" may be stretched over light stringers C which are supported in spaced parallel chordwise'arrangement upon the geodesics D. As will be understood; it is possible, by spacing the chordwise stringers C sufficiently closely, to produce a multi 'face ted' surface s proximating to a spherical--curvature as nearly as may be desired. One elementjofthe curvature; e. g; that revealed by a chordwise section in the: case of a wingor a longitudinal sectioninf'the' case; of a fuselage, is dictateden'tir'ely by tiie' shape of the stringers, whilst theother j element of" the" curvature, viz; that revealed; by alspanwiseisec j tion in the case of a wing'or a transverse section in the case of a fuselage, can be controlled'by ad ,iusting the degree of "fiatness'betweenthe string ers by the distension of the ribbonesurfaceundel" the outwardly directed resultant pressure.v

The attachment of: thefinterl'aced v Skill. to the. structure, and the operation: of. pre-stressing'thef constituent ribbons'A and B'tli'ereof, are'herein after more particularly exemplified with reference to a wing covering. Itwill. bev understood that similar methods may be; applied" to the skin of a fuselage or'of the; elevator, fin or'ot'her movable control surfaces; I I

In the case of a wing, each component ribbon A or B may pass continuously froman' attachment at the trailing edge of the upper'surface, around the nose of' theleading edgato an attachment. at the trailing edge of the lower sur face, and it is convenient to providemeans for adjusting at least one of such attachments in. order that the tension of the ribbons may be regulated to: the requisite degree; A- method of supporting the skin AB; at the requisite curvature in its passage around the leading edge off the;

wing is hereinafter described? with" reference to Figs; lI and1'2.

One means 'of' attaching the interlaced skin fabric'to the chordwise supporting stringers Cis depicted in- Figs: Rand 8: Said stringers are of I meansof clamping means F, F, in the manner shown in Fig. 6, and in relation to each ribbon B there is provided a small rotary spool G mounted in a fixed'bracketGil ina position inclinedto the'member'E so that the axis of rotation of said spool"G is perpendicularto' the axis of the ribbon B. The end'of eachribbon B is'passed through a-sl'otiin aspool G so that the ribbon may be tautened throughout its length when the spool is rotated by aconvenient key or spanner fittiug'on the squared end of'the spool. A ratchet wheel is fixed to-the axle of each spool G and arranged to cooperate with a suitable pawl or detent G3 in such manner as to hold the spool'when tightened;

Attaching and tensioning means similar to thoseillustratedin Figs. 4, 6 and 7 may be employed at the trailing edge longrons, the ribbons B being attached to adjusting spools G on the upper surface of the wing and the ribbons A beingattachedto adjusting spools G on the lower surface of the wing.

A simpler and (in some cases) more convenientmethod of attaching the ends of the ribbons A and-B tome-terminal frame-member (or trailing-edgeIong-ron) is shown in Figs. 9 and 10. Herethe member Eismade with a doublelongitudin'al recessEl' into which theen'ds of the rib bons A and B are pressed by means of a conforrm ably shap ed batten E2" which is held in place by means of screws and nuts E3. The action of tightening down said batten E2, and also the battens C5 of' theint'erme'diatestringers C where these-latter battens are used, serves to stretch the ribbons tightly across the structure, and it will be; evident that by suitably proportioning the overall lengths of the ribbons to the linear distance between the points at which the ends of the ribbons are attached to the longrons on the upper'and lower surfacesof the wing, the appropriate degree of" tension in the ribbons may be obtained.

The invention is especially, applicable to such airframe structures, e. g. wings, tail-planes and fins,'asarefprovided with de-icing equipment of the knownzkind" in which the heating medium (hotair-or exhaust gases) is conducted through a plenum or'd'uct', enclosed within the leading edge of the. structure. Such an arrangement is illustratedin Figs. 11" and 12 of the drawings, wherei-nthereference J'indicates a bulk-head and K a liner of corrugated metal plating. Said membersJ and K enclose the duct through which the'hotair or' gases-pass. The liner K is pierced at El to admit the heating medium unto the cavitiesL, 'L, whereby-itis positively directed into intimate contact with the, inner surface of the outer skin AB at" the leading edge'. In such a case; thefinterlaced ribbons A and B are passed over and around the said pierced corrugated liner K,*in contact with the upstanding parts of the corrugations thereof, so that the inner surface of the skin AB cooperates with the liner to constitute the cavities L as aforesaid. The liner K also serves to support the skin AB in the desired curved formation.

After the complete skin has been afiixed in position and tensioned, a succession of coatings or s'prayin'gs of a plastic sealing paint, such as polyvinyl chloride or metallic aluminium or the like, is applied over the outer surfaces of the interlaced ribbons A and B, each coating or spraying being rubbed down with a fine abrasive before the next is applied, until a hard, smooth finish is achieved. The finished skin is depicted at H in Fig. '1. Such a skin will be waterproof, fireproof and. capable of a substantial degree of fiexure under the working of the structure without cracking or flaking.

0 Although it would be possible to arrange the interlaced skin with one system of the component ribbons extending in the direction of the longrons and the other system disposed chordwise,

it is preferred by reason of the torsional rigidity thereby provided that the skin material be disposed in the surface at an angle to the longitu dinal axis of the basal structure. Conveniently, in a skin composed of two systems of metal ribbons interlacing at right angles to each other, sai'dskin isso applied to the structure that each system of ribbons lies at an angle of 45 to the longitudinal axis thereof.

By arranging the skin with its component ribbons at an angle to the longitudinal axis of the structure, and by tautening the ribbons to an appropriate degree, the skin is made to contribute considerably to the torsional rigidity of the entire structure, thereby affording a valuable increase in the efliciency of the skeleton frame owing to the consequent possibility of reducing the weights of its component members.

In the aforementioned alternative embodiment of the invention, in which the ribbon-systems are respectively arranged in longitudinal and chordwise directions, only the longitudinal ribbons are tensioned. As before, these will be made of high tensile steel, but the chordwise ribbons may be of a lightweight metal such as Duralumin (registered trade-mark). In this arrangement the longitudinal ribbons will conform throughout their length to the surface swept by the generators, and a nearly spherical curvature is obtained.

What I claim as my invention and desire to secure by Letters Patent is:

1. An airframe structure comprising a skeletal framework which includes a plurality of spaced chordwise stringers, a skin-like covering applied to said framework, said covering comprising thin metal ribbons interwoven after the fashion of the components of a woven fabric, and means for securing said covering to certain of said stringers, said last named means comprising a plurality of pairs of parallel slots formed in the stringers, through each respective pair of which one of the ribbons comprising the covering is threaded.

2. An airframe structure comprising a skeletal framework work includes a plurality of spaced chordwise stringers, a skin-like covering applied to said framework, said covering comprising two systems of thin metal ribbons interlaced at right angles to each other after the fashion of the components of a woven fabric, and disposed so that each ribbon lies at substantially a 45 angle to said stringers, and means for securing said covering to certain ofsaid stringers, said last named means comprising two series of pairs of parallel slots formed in the stringers, through each respective pair of which one of the ribbons comprising the covering is threaded, the slots of one of said series of pairs being disposed at angles,

of 45 with the length of the stringers and receiving the ribbons of one system, and the slots of the other series being disposed at right angles to the slots of the first named series and receiving the-ribbons of the second system.

3. An airframe structure which comprises a skeletal framework including a terminal member, a skin-like covering applied to said framework which covering comprises thin metal ribbons interlaced after the fashion of the components of a woven fabric, the ends of at least some ofthe ribbons beingadjacent said terminal member, means for securing said ribbons to said frame work and adjusting the tension thereof, said means comprising spools mounted for rotation on said terminal member, the ends of said ribbons being wound respectively upon said spools, means for rotating said spools to impart the required degree of tension to the ribbons comprising the covering, and detent means for retaining said spools in their adjusted positions with the ribbons under tension.

4. An aeroplane wing comprising a skeletal framework including a trailing-edge longron on the upper surface and a trailing-edge longron on the lower surface, a skin-like covering for said wing comprising a plurality of thin metal ribbons interlaced after the fashion of the components of a woven fabric, certain of the ribbons composing the covering terminating adjacent to 5. An aeroplane wing comprising a skeletal I framework including a trailing-edge longron on the upper surface and a trailing-edge longron on the lower surface, a skin-like covering for said wing comprising two systems of thin metal ribbons interlaced after the fashion of the components of a Woven fabric, the ribbons of the respective systems being disposed at right angles to each other and at angles of substantially 45 with the major horizontal axes of the wing, ribbons of each system terminating adjacent to and being secured to the trailing-edge longron on the upper surface and extending diagonally forwardly along the upper surface of the wing, around the nose of the leading edge of the wing, and diagonally along the lower surface thereof,

and the opposite ends of said ribbons being secured to the trailing-edge longron on the lower surface of the wing.

6. In an airframe construction, which includes a skeletal framework or substructure, in combination, a flexible outer skin applied to said substructure, said skin comprising two or more sysamJlyin-g= and; maintaining tension insaid skin.

in both' of two. directions inthe plane thereof.

7. In an airframe construction, which includes a skeletal framework orsubstructure, in combination, a. flexible outer skin applied to said.

substructure, said skin comprising two or more systems of thin metal ribbons interlaced after the fashion ofthe components of a woven fabric, but relatively movable with-respect to each other toaccommodate any difierential tautening of, the ribbons of the respective systems, said component ribbons being. disposed closely together to formasubstantially continuous surface, the ribbons of, each of said systems being disposed at an angle of approximately 90 with the ribbons of the other system and at an angle ofapproximately 45 with the longitudinal axis of the construction, and means forming a permanent part of. the construction for applying and maintaining tension. in said skin in both of two directions in the, plane thereof.

8. In an'airframe constructiomwhich, includes a skeletal framework or substructure, in combination, a flexible outer skin applied to said substructure, said skin comprising two or. more systems of thinmetal ribbons interlaced after the fashion of thecomponents of a woven fabric, but

relatively movable With respect to each other toaccommodate any differential tautening of the ribbons of the respective. systems, said component ribbons being disposed closely together to formal substantially continuous surface, the rib- 8,; bons of each of said systems-beingdisposed at-an. angle of approximately 90 with-the ribbons-oil the other system and at an angle :of approximate-5 1y 45 with the longitudinal, axis-of the construca tion, and means forming a permanentspart oil the construction for applying and;maintaining, each of the ribbons comprising; saidsystems, in dividually under tension in directions IQIIE'itRdiL- nally of said. ribbons;

BARNES NEVILLE 'WALLIS.

REFERENCES CITED The following references are of! recordin-the: file of this patent:

UNITED STATES. PATENTS Number Name Date;

1,243,041 Clark Oct. 16, 1916, 1,322,348 Rosenhain et al. Nov 18,1919, 1,409,982 Walen ,Mar'.l2:1; 1922; 1,426,626 Belcher Aug. 22; 1.922 1,717,390 Kucher -1--- June.l8-, 1929; 1,985,649 Wallis Dec; 25; 19334 v 2,344,131 Coryell Mar; 14, 1944;

FOREIGN PATENTS Number Country Date.

125,669 Great Britain May 1, 19.19; 142,082 Great Britain May-1,1921. 264,546 Great Britain Jam 25; 1927? 479,839 Great Britain Feb-811938

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